Water purification method and apparatus

ABSTRACT

An improved method and apparatus for continuously agglomerating solids of colloidal size or larger suspended in a liquid is disclosed. The process comprises passing the liquid between spaced electrode plates in the presence of a fluidized bed of conductive particles, and subjecting said liquid suspension to an electric field from alternating current applied across said electrodes through the conductive particles of said bed. The turbulence of the particles in said bed has been found to improve conductivity and current efficiency, minimize electrode erosion, and by a mechanical, scrubbing action of the bed particles, minimize fouling or scaling of the electrodes so that the suspending forces of said solids are rapidly and efficiently broken. The agglomerated solids may then be separated from the liquid by conventional means such as skimming, settling, flotation and the like.

This is a division of application Ser. No. 663,790, filed Mar. 4, 1976now U.S. Pat. No. 4,094,755, which is a continuation-in-part of mycopending patent application Ser. No. 613,289, filed Sept. 15, 1975,which application in turn was a continuation of application Ser. No.487,730, filed July 11, 1974. Accordingly, the disclosures of my saidapplications Ser. No. 613,289 and Ser. No. 487,730, filed Sept. 15,1975, and July 11, 1974, respectively, are hereby incorporated byreference.

The prior art contains a variety of different processes wherein directcurrent, or direct current having alternating currents superimposedthereon, is utilized to agglomerate solids suspended in aqueous liquid.U.S. Pat. No. 3,767,046 to Hartkorn is exemplary thereof.

These prior processes incorporate many disadvantages which tend torender them either economically unfeasible or very expensive to operate.For example, prior direct current agglomeration processes arecharacterized by rapid deterioration of the anode and/or scaling orfouling thereof with organic materials from the solution, impuritiesfrom the metal itself, or impurities resulting from grain reactions atthe anode surface. Therefore, batch operation is required due to thenecessity for frequent shut down to clean or replace the anode, andcontinuous operation, or operation for extended periods of time isimpossible.

A variety of cell additive materials are known in the art for reducingthe tendency of the electrodes to scale, to improve current efficiency,and to prolong electrode life. These additives are effective in varyingdegrees. However, the expense involved in utilizing additives issubstantial and is a definite disadvantage in direct current operation.Furthermore, as will be obvious to those skilled in the art, continuousoperation or at least semi-continuous operation over a prolonged periodof time without the need to shut down to replace or clean the anode ispreferable from an economic standpoint to batch operation even withadditives.

The aforementioned related patent applications describe a method foragglomerating suspended solids in an aqueous solution which method ischaracterized by the efficient use of alternating current, alone, toprovide continuous operation without the necessity to frequently replaceor descale the anode. Alternating current has been found to exert anelectrostrictive effect on the suspended materials. In addition,alternating current continuously produces hydrogen peroxide at bothelectrodes which tends to maintain said electrodes in clean conditionduring operation. Finally, the hydrogen produced on the electrode hasthe capability of reacting with the electrode itself to produce,ultimately, minimal quantities of metal hydroxides which act asflocculation seeds to promote flocculation or agglomeration of the solidimpurities. The electrostrictive effect and the production of hydrogenperoxide at each electrode are not possible in a direct current cellwithout the presence of sulfate radicals or other additives.Accordingly, said process is characterized by much more efficientoperation in a continuous mode, without the necessity of using costlyadditives.

It has now been discovered that if the aqueous solution containingsolids to be agglomerated is passed between electrodes on a continuousbasis in the presence of a fluidized bed of conductive particles, vastlyimproved agglomeration or flocculation of said solids results from themultiplicity of electrolytic cells presented in the collapsing field ofalternating current. In addition, by utilizing conductive particleswhich are substantially resistant to attrition, a mechanical scrubbingeffect will be exerted upon the electrodes which will tend to keep saidelectrodes clean during continuous operation and thereby avoidingfrequent shut downs for descaling. Furthermore, it has been discoveredthat by utilizing the process of this invention electrode erosion isreduced to approximately 0.2 percent of that found in direct currentprocedures.

Accordingly, the process of this invention by utilizing a turbulentfluidized bed of conductive particles achieves the advantage ofcontinuous operation with high current efficiency.

It should be noted that the fluidized bed may be established in the cellof this invention with the process water alone, or with the processwater augmented by a gas such as air injected into the vessel. Once afluidized state has been established, the likelihood of bridging, shortcircuits and the like between the electrodes is eliminated. Increasedturbulence then increases the efficiency of the process of thisinvention with the upper limit thereof to be governed only by theprocess economics. water augmented by a gas such as air injected intothe vessel. Once a fluidized state has been established, the likelihoodof bridging, short circuits and the like between the electrodes iseliminated. Increased turbulence then increases the efficiency of theprocess of this invention with the upper limit thereof to be governedonly by the process economics.

In an embodiment of this invention, gas assisted turbulence is aided bydisposing the side wall of the cell vessel at an angle to the verticalaxis of said vessel. The angled side walls then increase the ease withwhich a true fluidized bed may be established within the vessel andincrease the scrubbing action against the electrode faces by the bedparticles.

Under the alternating current electric field, the conductive particlesbecome, as noted above, bipolar electrodes so that the cell contains amultiplicity of said electrodes with each electrode providing its ownboundary layer. The particle movement inherent in the fluidized bed notonly ensures a continuous scrubbing or cleaning of the electrode faces,but of the individual particles and their boundary layers. Accordingly,the maximum turbulence consistent with a given apparatus will providethe maximum efficiency achievable according to the process of thisinvention.

As in the aforementioned patent applications, it is preferred to utilizealternating currents having a frequency of between 0.2 and 800 Hz acrossthe electrodes generating an electric current having a magnitude ofabout 0.08 to 6.0 ampheres per square inch through said bed. Inaddition, however, it is also preferred to maintain a residence time insaid bed of between nine and twenty-five seconds and a spacing of saidelectrodes of between about one-quarter and two inches and mostpreferably about one-half inch. The spacing between the electrode faces,however, may be greater than two inches, if desired. However, it ispreferred to utilize a spacing of about one-half inch, and multiplecells in parallel to accomodate the volume of process water desired.

Accordingly, it is an object of this invention to provide an improvedprocess for agglomerating solids suspended in an aqueous liquid bypassing the liquid to be processed through an alternating currentelectric field while maintaining a turbulent condition thereof for thegeneration of hydrogen peroxide at each electrode.

It is another object to provide a process whereby solids suspended in anaqueous solution are agglomerated by exposing said solids to a fluidizedbed containing conductive particles subjected to an alternating currentfield.

It is another object to provide a process whereby said suspended solidsare agglomerated by the action of a multiplicity of electrodes in acollapsing alternating current field in a turbulent fluidized bed ofconductive particles whereby the suspension forces are broken and saidsolids cause to clump, agglomerate, or flocculate.

It is yet another object to provide an apparatus for agglomeratingsolids suspended in a liquid comprising spaced electrodes with a sourceof alternating current coupled thereto in a vessel with a turbulentfluidized bed of conductive particles disposed therebetween.

It is still another object to provide an apparatus for agglomeratingsolids suspended in a liquid including a fluidized bed of conductiveparticles subjected to an alternating current from spaced electrodes oneither side thereof whereby a turbulent condition is maintained in saidbed and a multiplicity of electrodes are provided by the particlestherein to exert the effect of a multiplicity of electrodes on saidsolids and to thereby disband the suspending forces and cause saidsolids to clump together so that they may be separated from the liquidby conventional techniques.

It is yet another object to provide a fluidized bed vessel havingopposed, spaced electrode faces and side walls disposed at an angle tothe vertical axis thereof whereby the bed may be maintained in aturbulent condition to thereby exert a scouring effect upon theelectrode faces to minimize scaling of impurities thereon.

These and other objects will become readily apparent with reference tothe drawings and following description wherein:

FIG. 1 is a plan view of an apparatus preferred for utilization of theprocess of this invention;

FIG. 2 is a vertical sectional view of the vessel portion of theapparatus of FIG. 1 having the center portion removed;

FIG. 3 is a sectional view taken along lines 3--3 of FIG. 1;

FIG. 4 is a sectional view taken along lines 4--4 of FIG. 2;

FIG. 5 is a sectional view taken along lines 5--5 of FIG. 2;

FIG. 6 is a sectional view taken along lines 6--6 of FIG. 2;

FIG. 7 is a sectional view taken along lines 7--7 of FIG. 2;

FIG. 8 is a sectional view taken along lines 8--8 of FIG. 2;

FIG. 9 is a graph representing the efficiency of the process of thisinvention as measured by percent transmittance versus residence time ina vessel of this invention;

FIG. 10 is a graph representing current density versus residence time,current consumed, and flow rate;

FIG. 11 is a graphical representation of the relationship between theamount of process water treated and current density versus the velocityand flow rate;

FIG. 12 is a graphical representation of the cell resistance as graphiteparticles are added to water for both alternating current and directcurrent;

FIG. 13 is a graph representing the temperature in the cell withrelation to the cell resistance in a situation wherein there is no fluidbed, and a situation wherein there is a fluidized bed within said cell;

FIG. 14 is a graphical representation of the linear flow rate versus bedheight for establishing fluidization with different particle bedconstituents.

With reference to the drawings, FIG. 1 represents a preferred version ofan apparatus of this invention for processing aqueous liquids containingsuspension of solid materials. The apparatus includes a vessel 10 whichmay contain any desired number of cells such as two as illustratedherein (see FIG. 3), and as will be subsequently described. Each cell 12in vessel 10 is controlled through a console 14. Console 14 is utilizedto monitor and regulate the turbulence in the cell and to apply thedesired current and voltage to the electrodes. The console 14 may becoupled to a source of electrical energy by, for example, a cable 16,and supplies the desired voltage and current to the cell electrodesthrough cables 18. It will be obvious to those skilled in the art thatconsole 14 is not an essential feature of this invention, and individualcontrol may be utilized.

Turbulence, as noted previously, may be established by the process wateradmitted to the cell, or may be augmented with a gas such as air. In thecase of a multiplicity of cells, it is preferred to provide a separatewater inlet and air inlet for each cell. Accordingly, as shown in FIG.1, process water is pumped through a conduit 20 to cell inlets 22 and22' in the lower portion of the vessel 10. The flow of process water maybe monitored, for example, by flow meters 24. The gas for augmenting thefluidized bed condition within each cell, which in the preferredembodiment is air, is pumped to the lower portion of each cell throughconduit 26 and admitted through inlets 28 and 28'. Console 14 maycontain a variety of meters, gauges and the like for regulating the flowand monitering the flow into cells 12. The vessel 10 also includes anoutlet 28 in the upper portion thereof for the water with agglomeratedsolids which has been processed according to the process of thisinvention. Water with solids exiting outlet 28 may be conveyed byconventional means to any desired separating device such as a settlingtank, centrifuge, skimmer, flotation cell, or the like.

With attention to FIG. 3, the vessel 10 comprises in this embodimenttwin cells 12 housing opposed electrodes 30. Electrodes 30 are separatedby an insulating spacer 32, and are supported by side walls 34 and facewalls 36. The inner electrodes are also separated by an insulatingspacer 38.

The electrodes in each cell 12 may preferably be of any non-valve metalsuch as aluminum, magnesium or steel. For most applications, however,aluminum will be preferred. The opposed electrodes are spaced, as notedabove, a distance from about one-quarter to at least two inches, butpreferably about one-half inch apart. Any number of cells 12 may beutilized in vessel 10 as preferred from one or two as shown in FIG. 3 upto ten or more. In each instance, the electrodes will preferably bedisposed in parallel.

While the upstanding side walls 34 of vessel 10 may be vertical, it ispreferred to have the walls disposed at an angle thereto. Preferably theangle will be between five and thirty degrees to the vertical and mostpreferably ten degrees. The angle of side walls 34 as noted above isintended to facilitate the establishment of a turbulent fluidized bedwithin each cell 12. Electrodes 30 extend substantially the entirecentral portion of vessel 12 nearly coextensive with the angled sidewalls 34.

With attention to FIGS. 2, 4, 5, and 7, an inlet chamber 37 is disposedin the base 39 of vessel 10 for mixing the process water admittedthrough inlets 22 and 22' and the air may be admitted through inlets 28and 28' into mixing chamber 42 to establish the desired turbulence. Ascreen 40 is disposed above the inlet chamber 37 and below the mixingchamber 42. A screen 44 is also disposed above mixing chamber 42 to, aswill be subsequently described, support the fluidized bed and maintainit confined to the central portion of vessel 10 between the angled sidewalls 34. The side walls 46 of the lower portion 39 of vessel 10 may bevertical as shown. Vessel 10 may be supported on a base 48, as desired.

With attention to FIGS. 2, 6, and 8, the upper portion 50 of vessel 10houses an upper disengagement chamber 52 disposed above electrodes 30. Ascreen 54 is disposed above chamber 52 to maintain the fluidized bedwithin vessel 10. Electrode leads 56 extend from electrodes 30, and areadapted to be coupled to cables 18 connecting the electrode 30 withconsole 14 and the source of electrical energy transmitted therethrough.

As process water passes upwardly through screen 54, a weir 58 isprovided which separates the interior of vessel 10 from an outletcollection chamber 60 wherein the processed water 62 is collected forremoval through outlet 28. The processed water from outlet 28 is then,as noted above, transported by any conventional means to a solidseparation device such as a skimmer, settling tank, centrifuge, or thelike (not shown). In the alternative the processed water may be recycledthrough inlet 20 in vessel 10 with the agglomerated solids serving asflocculation seeds to achieve greater purity.

The side walls 64 and front and rear walls 36 may be integral with thecorresponding side and front and rear walls of the central portion ofvessel 10, or may be welded thereto. Said walls may be of any desiredconfiguration adapted to form chamber 52, and outlet chamber 60 as willbe obvious to those skilled in the art.

The exact particle size of the constituents of the fluidized bed is notcritical, and may range from about three millimeters to up to aboutone-fourth inch. On the basis of tests conducted, to achieve bedstability at a residence time desired, the ideal particle would be asphere of approximately one-eighth inch diameter and a specific gravityof approximately two. The material utilized, however, could be anyconducting material which has excellent mechanical and chemicalstability. It is preferred, however, that the bed of particles becapable of true fluidization. Absent a fluidized bed condition, as notedabove, bridging and short circuits can result which may diminish currentefficiency. In a preferred version of this invention, a graphite pelletis utilized which was cylindrical and nominally 0.125 inches in diameterby 0.19 inches long, with a specific gravity of 2.1. The cylindricalpellets were found to enhance the turbulence of the fluidized bed, andto increase the electrical effect thereof.

FIG. 14 illustrates the results of tests directed to establishing afluidized bed in a tube having an inside diameter of 5/8 inches, filledwith possible bed constituents. Each was fluidized with water at thevarious velocities shown, and the bed height relative to velocity isillustrated in FIG. 14.

A series of tests was also conducted utilizing a cell having parallelside walls and an electrode plate spacing of 0.403 inches to evaluatethe conductivity of the graphite particles selected relative totemperature in a fluidized bed, and alternatively in a condition whereinfluidization is not established. It was found that, for example, at awater flow rate of 1.5 gallons per minute and an air flow rate of 0.2SCFM, the bed was expanded from a "no flow" height of 153/4 inches to acompletely fluidized height of 32 inches. Dramatic flocculation occurredwith a current density of 0.19 amps per square inch and a powerconsumption equivalent to 3.11 kwhrs per 1000 gallons. Significantlylower power consumption was experienced with said fluidized bed comparedwith the power consumption experienced with no bed as shown in FIG. 13.

FIG. 12 also illustrates cell resistance as graphite pellets are addedto 225 ccs of water to illustrate the greatly increased conductivityfound with alternating current as compared to direct current in afluidized bed environment.

FIGS. 9-11 illustrate the results achieved in tests conducted in thedevice of FIGS. 1-8 wherein the plate spacing was one-half inch betweenelectrodes, and the bed volume was about two-thirds of the actual volumebetween the electrodes. In addition, the side walls were disposed at aten degree angle to the vertical.

With attention to FIG. 9, this graph depicts efficiency of the device ofthis invention as compared to residence time for the liquid beingprocessed. Efficiency is measured as the percent of light transmittanceas measured with a spectrophotometer at λ=5500 A° with distilled wateras a standard equalling 100 percent. Thus, the efficiency, or percenttransmittance, measures the clarity of the water processed as comparedto distilled water. While the water processed in this example, theresults of which are depicted in FIG. 9, was white water paper milleffluent, the results are representative for other liquids processed. Asshown therein, the optimum residence time should fall in the linearportion of the graph between about nine and twenty-five seconds. Alonger residence time achieved little increase in transmittance ascompared to the current required. Accordingly, residence time in thedevice of this invention is preferred between nine and twenty-fiveseconds total.

The following are exemplary results achieved utilizing the device ofthis invention:

The device of this invention has been used to treat a variety of wasewaters including coke oven flushing liquor, well water containingcolloidal iron, and process water containing colloidal graphite papermill kraft and soda mill waters, machine shop oil in water emulsions,cheese whey, copper drawing soap effluent, domestic sewage, paper milllagoon sludge, and various other commercial and domestic waste streams.In all cases suspended solids were significantly reduced within thepreferred residence time as above noted.

The following are specific examples utilizing the process of thisinvention. In each the fluidized bed was established with graphitepellets having a specific gravity of about 2.1.

EXAMPLE I

A flow rate, total, of 3.5 to 5 gpm of colloidal graphite contaminatedwater and an air flow rate of one to 1.5 SCFM in the two cell vessel ofFIGS. 1-8 was used to establish good fluidization with cylindricalgraphite pellets as described above having a specific gravity of about2.1. A total current of 30 amps, a voltage of 50 VAC and 60 Hz wasapplied across the electrodes and the colloidal suspension was "broken."Suspended solids were reduced from 1285 ppm in the untreated water to 38ppm after one pass through the unit followed by approximately two hourssettling time in a holding tank, not shown. The influent water was at atemperature of 34° to 38° F. Higher influent temperatures wouldobviously result in a higher conductivity, e.g., as a general rule waterat 70° F. has a conductivity of 2 to 3.75 that of water at 32° F.depending on the amount and type of impurities.

EXAMPLE II

Paper mill lagoon sludge was processed in an apparatus of this inventionas described in FIGS. 1-8. The sludge had originally been treated withaluminum sulfate but contained suspended solids which under normalconditions would remain suspended for years. The sludge had a very highviscosity and zero percent transmittance. The suspended solids amountedto 5.4 percent by weight, and the aluminum hydroxide equalled 1.3percent of the solids.

The sludge was diluted 3:1 with city water. The flow rate of the deviceof this invention was three gallons per minute, 60 amps current and 60VAC were applied across the electrodes.

The processed sludge contained solids which precipitated within tenminutes and the suspension forces were totally broken. The transmittanceof the supernatant of the processed sludge after one hour was measuredat 86.5 percent at 475 mu. Suspended solids remaining were measured at11 ppm.

In summary then it has been discovered that alternating current appliedthrough a turbulent fluidized bed of conductive particles willefficiently and economically reduce solids suspended in water on acontinuous basis. The turbulence established increases currentefficiency, and contributes to an electrostrictive effect whereby amultitude of bipolar electrodes are established within the cell to breakdown the suspending forces of the solids. The solids then clump togetherwhereby they may be easily removed by settling, skimming, or the like.

In contrast to prior art procedures, by utilizing alternating currentthe electrode surfaces remain relatively clean for efficient, continuousoperation due primarily to the generation of hydrogen peroxide, and amechanical scrubbing action by the bed particles. The hydrogen peroxideas will be obvious to those skilled in the art also contributes todecolorization and deodorization of the water processed. Mostimportantly, however, alternating current allows continuous operationwithout the need to shut down and replace a sacrificial anode, or todescale the anode, and does not require costly additives for efficientoperation.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is, therefore, to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are, therefore, intended to be embracedtherein.

What is claimed and desired to be secured by United States LettersPatent is:
 1. An apparatus for purifying water to agglomerate solidssuspended therein for subsequent removal comprising:a vessel havingfront, rear, and side walls, and having an inlet therein for admittingwater to be purified and an outlet for water and agglomerated solids,the side walls of said vessel lying in a plane disposed at a verticalangle to the horizontal axis of said vessel; at least one pair ofupstanding electrodes disposed within said vessel between the inlet andthe outlet, said electrodes having opposed, spaced, metal faces definingwith the side walls of said vessel a water treatment chamber, saidchamber being in communication with the vessel inlet and outlet; meanscoupled to said electrodes for applying an alternating current theretoof a frequency of from 0.2 to 800 Hz with a current density of 0.08 to 6amps per square inch; means carried by said device for directing waterto be purified through the inlet into said vessel, through the treatmentchamber and subsequently for directing treated water from said vesselthrough the outlet; means carried by said device for agitating the waterto be purified, within the treatment chamber, to maintain said water inturbulence while said water is disposed between said electrodes;conductive means disposed within said chamber between said electrodesfor enhancing the alternating electrical field across said electrodeswhen water to be purified is disposed within said chamber.
 2. The deviceof claim 1 wherein said side walls be in a plane disposed at an angle tothe vertical axis of said vessel of up to 30°.
 3. The device of claim 2wherein said angle is from 5° to 30°.
 4. The device of claim 3 whereinthe angle is about 10°.
 5. The device of claim 1 wherein the opposedfaces of said electrodes be in planes parallel to the vertical axis ofsaid vessel.
 6. The device of claim 1 wherein said means for agitatingincludes a source of gas under pressure in communication with saidchamber adapted to be injected thereinto.
 7. The device of claim 6wherein the gas is air.
 8. The device of claim 1 wherein said conductivemeans comprises graphite pellets.
 9. The device of claim 1 wherein theface of said electrodes is a metal selected from the group consisting ofaluminum, iron, steel, and magnesium.
 10. An apparatus for purifyingwater to agglomerate solids suspended therein for subsequent removalcomprising:a vessel having an inlet for admitting water to be purifiedand an outlet for water and agglomerated solids; at least one pair ofmetal electrodes disposed within the vessel having facing surface areassubstantially closely spaced, said electrodes being disposed between theinlet and the outlet of said vessel; means coupled to said electrodesfor applying an alternating current thereto of a frequency of from 0.2to 800 Hz. with a current density of 0.08 to 6 amps per square inch;means carried by said device for directing water to be purified throughthe inlet into said vessel, between said electrodes, and subsequentlyfor directing treated water from said vessel through the outlet;particulate conductive means disposed within said vessel between saidelectrodes for enhancing the alternating electrical field across saidelectrodes when water to be purified is disposed therebetween; meanscarried by said device for agitating the water to be purified and theparticulate conductive means wherein said water to be purified isdisposed between said electrodes in the alternating electrical fieldthereacross to maintain said water in turbulence while said water isdisposed between said electrodes.
 11. The device of claim 10 wherein theopposed faces of said electrodes extend parallel to the vertical axis ofsaid vessel.
 12. The device of claim 10 wherein said means for agitatingincludes a source of gas under pressure in communication with theinterior of said vessel and adapted to be interjected thereinto.
 13. Thedevice of claim 12 wherein said gas is air.
 14. The device of claim 10wherein said particulate conductive means comprises graphite pellets.15. The device of claim 10 wherein the face of said electrodes is ametal selected from the group consisting of aluminum, iron, steel, andmagnesium.